The 7.3W/120V windowsill heat mat is perfect for veteran growers, beginners, and children too. It is the perfect size for small growing spaces, and improves germination by warming the root area 10 deg. to 20 deg. F. over ambient temperature. By warming the roots you increase the growing success, as this mat will maintain a controlled temperature all season long. Dimensions: 3" W. x 20" L.